This invention relates to method of measuring the stretch of conveyor belt, and particularly to a method of measuring the value of the stretch in a joint of a conveyor belt, in which opposite end portions of the belt having embedded therein steel cord cores in the longitudinal direction thereof are joined to each other to provide an endless belt.
Conveyor belts have been widely used in which opposite end portions of the belt have embedded therein steel cord cores joined to each other to provide an endless belt. The joint of the conveyor belt of the type described has been of such an arrangement steel cord cores exposed from opposite end portions of the belt are overlapping alternated with each other. Thereafter, a rubbery material is filled in the portion, where the steel cord cores are exposed and vulcanized for bonding, thereby joining the opposite end portions of the conveyor belt to each other. The endless conveyor belt thus formed has the forward and rear end portions wound around rotary driving members and is driven thereby, so that the conveyor belt is subjected to opposite tensile forces which cause the aforesaid joint to be pulled in directions tending to disconnect it.
When the tensile forces are applied to the joint, the steel cord cores at the respective end portions of the conveyor belt in the joint are pulled in directions opposite to each other. Because of this, if the conveyor belt is used for a long period of time, stretch occurs in the joint and, depending upon the conditions of use, it is possible for the tip ends of the steel cord cores to break through the rubber layer and project therefrom, and for the joint to be disjoined, thereby breaking the conveyor belt down. Consequently, it is necessary to constantly monitor the progress of the stretch in the joint of the conveyor belt.
Heretofore, the prior art methods of monitoring the progress of the stretch in the joint of the conveyor belt have been such methods that rely on a visual inspection for external flaws and the value of wear of the rubber, to infer the internal conditions of the joint. In other prior art methods, marks are provided at two points interposing the joint therebetween, the distance across the two marks is periodically measured and the progress of the stretch in the joint is ascertained through variation in the aforesaid distance.
Nevertheless, the conventional methods of measuring the stretch in the joint of the conveyor belt as described above present disadvantages, in that the operation of the conveyor line should be interrupted everytime the measurement is performed, thereby requiring large amounts of labor, and resulting in decreased production efficiency. Further, in the methods described above, the measuring work principally relies upon visual inspection, thus presenting disadvantages stemming from the wide dispersions in pass-fail judging made by the measurers. Consequently, accuracies in measurement are rather low.